1. Field of the Invention
The present invention relates to a lower inertial compact disk driving device, and particularly to a lower inertial compact disk driving device, wherein an optical unit device is used as a medium of the laser beam, thereby, the optical spot is traced more instantaneously and precisely on a disk through a tracing device.
2. Description of the Prior Art
In the current compact disk driving device, the disk rotates and the laser head makes a straight and reciprocal movement. The prior technical lower speed compact disk drive uses a constant linear velocity (CLV) or constant angular velocity (CAV). The laser head has the constant speed as reading data. Another conventional way is used to increase the reading speed by increasing the rotation speed. Some current compact disk drive and DVD ROM use xe2x80x9cTrue Xxe2x80x9d multi-beam technology, which is used to assure the reading in the whole disk has the same speed. The speed changes only when the mass of the compact disk and the operation system are different.
The technologies for reading DVD are not the same in different kinds of compact disk drives. In the prior art, to be compatible with the common CD ROM, the DVD ROM uses two heads technology to realize the auto adjustment of the servo unit device of a compact disk driving device so that the accuracy of reading data is improved. Double dynamic shock suspending (DDSS) system is used to effectively reduce the shock as a compact disk drive rotates with a high speed. Auto balance system (ABS) is used to retain the disk to be horizontal so that the reading ability of the compact disk is improved. Automatic intelligent error correction is used so that the reading amount of a disk is improved greatly. The above said many technologies cause the performance of a compact disk driving drive to be improved. However, current compact disk driving device uses a high rotation speed disk and a laser head of straight and reciprocal movement. The inertial of the disk is too large and the mass of the laser head is large. Therefore, the current used compact disk driving device consumes much power and has a large shock so that the moving range of the disk is confined. For example the current compact disk drive cannot be used in a personal digital assistant (PDA), which has the function of calculation, phone, facsimile, network, etc. These functions can be realized wirelessly. The extra equipment of PDA consumes low power. However, current compact disk drive has large rotation inertia and the laser head is heavy and thus cannot realize the object of lower power consumption.
Furthermore, due to the inner shaft hole of compact disk is biased and there is a gap existed to compensate for expansion and contraction, the central error will be produced when installing compact disk, and due to further gap of bearing, the tunnel and the rotary axle are not concentric and cause the tunnel to displace along the radial. Besides, the contraction rate in various directions of the compact disk is different so as to produce deformation. Thus, the major object of radial tracking servo is to drive the optical head to move from current track to target track in a least time while retaining the interference in tunnel center between tunnels and reducing the signal voltage.
Due to the effects that the information lines of compact disk drive is spiral and the compact disk and station are not concentric, the beam emitted to the information lines will depart from the race information lines continuously during read/write process. According to the analysis and research, to read/write the information correctly, while ensuring the precision focusing, the tracking error must be controlled within xc2x10.1 xcexcm. Only if the deviation of the center of the beam emitted on read/write information lines is less than 0.1 xcexcm, the read data can be ensured correctly. However, practically, due to the compact disk and station deviation may be up to 70 xcexcm, a close loop focus control loop must be used to achieve high precision tracing. The methods for detecting radial error signal of traditional optical head are numerous; the commonest are three light beam method, push-pull method, etc. In holographic lens, radial tracking servo generally uses push-pull method. However, the present technical focusing device is installed on the laser head and moves straightly and reciprocally with laser head. Since the focus coil is heavy, the straight and reciprocal movement will cause a large instantaneous speed and thus a large electric power is consumed.
Accordingly, the primary object of the present invention is to provide a lower inertial compact disk driving device wherein in operation, the laser head and the disk are static. A displacing device is used to change the position of the laser beam incident upon a disk.
Another object of the present invention is to provide a lower inertial compact disk driving device, wherein the focus of the laser beam from the laser head is precisely located at the optical recording surface by a precise tracing unit device. The focus of the laser beam emitted from laser head can move precisely form current track to target track.
A further object of the present invention is to provide a lower inertial compact disk driving device, wherein a close loop focus control loop is used, and light spot detect method is used to detect servo signal. The focusing servo signal is phase and amplitude compensated and then is amplified so as to drive a focusing device to control the movement of a focusing lens and thus optical spot is radiated to a disk precisely.